The goal of this research is to empirically assess the three year effects of the ?CATCH My Breath? (CMB) program on delaying the onset of e-cigarette use with a 6th?8th grade cohort, using a 20-school group randomized controlled trial (RCT), with 1,400 students. E-cigarettes have grown in popularity and are the most commonly used tobacco product by US youth. Based on 2017 Monitoring the Future estimates, we project that 1.6 million middle school students will have ever tried an e-cigarette. Flavors such as candy and fruit are appealing to youth and play an important role in encouraging nonsmokers (and smokers) to try them. Although e-cigarettes are less harmful compared to combustible tobacco use, they contain nicotine, which is highly addictive. Recent research, including a 2017 meta analysis, strongly suggests that youth who only smoke e-cigarettes exhibit symptoms of addiction, and over time, are more likely to experiment with and use combustible tobacco. To avoid the possibility of nicotine addiction, nonsmoking youth should be educated about this health threat and discouraged from experimenting with e-cigarettes. Unfortunately, few e-cigarette prevention programs exist, and none tested for long-term efficacy. In addition, although some tobacco prevention programs have included an e-cigarette component, to our knowledge, none of these revised programs have been formally evaluated. The lack of e-cigarette specific program content, and rigorous evaluation, warrants the proposed project. CMB was developed and custom built with input from school administrators, health education coordinators, tobacco prevention educators, classroom teachers, students, and parents. CMB has been formatively evaluated and pilot tested at 59 middle schools in 7 states, resulting in positive feedback from over 100 middle school teachers and 9,578 6th?8th grade students. Our second pilot test was a pretest-posttest controlled experiment (2017-2018), and resulted in an treatment-control difference of 3.8% in ever smoking over a 16-month period. Finally, the research team, with the CATCH Global Foundation, have developed a digital school-health program distribution framework which includes in-person or on-line teacher training (https://catchinfo.org/modules/e- cigarettes/). Using this framework, CMB can be delivered to teachers at very low cost, eliminating cost and access to program materials as major barriers to program implementation. Given CMB?s current popularity with schools as a ?best practice? program, and with initial positive results, a full scale randomized control trial is needed to determine longer term, 6th-8th grade efficacy.